Description: LMT proposes to develop two novel microfluidic innovations: (1) a novel long-path (250-mm), folded, on-chip absorption cell utilizing lock-in amplified detection to enable high colorimetric sensitivity; (2) a novel on-board system for mixing reagents and standards from dry chemical constituents to enable their in-situ preparation thereby enabling long-duration deployments where pre-mixed consumables would have otherwise degraded. These two innovations will enable the construction of the In-situ Nitrate/Nitrite Analyzer (INNA), a deployable microfluidic system for the continuous, autonomous, long-duration analysis of nitrate and nitrite in natural waters that will feature unprecedented sensitivity and autonomous deployment durations for this class of robust microfluidic system. INNA will be able to detect nitrate and nitrite down to single-digit nano-molar levels, making the instrument suitable for monitoring nutrients even in the oligotrophic open ocean where levels of these compounds can be below 10 nM. The system will rely upon the well-understood and widely-used colorimetric Griess assay for nitrite.

Benefits: INNA itself is highly-relevant to NASA research involving nutrient cycling in the oceans, such as the study of phytoplankton and carbon sequestration from the atmosphere as nitrate is often a limiting resource for the growth of autotrophs. Because INNA is being designed for high sensitivity and long-duration deployments, it is suitable for making an instrument network so global ocean nitrogen cycling could be studied, potentially informing upcoming missions such as the Aerosol/Cloud/Ecosystems (ACE) mission. Additionally, the colorimetric approach taken with INNA, including the on-board of dry chemical reagents and standards, would allow for future incarnations of the instrument to be deployed on other planets, moons, or small bodies such as comets. The colorimetric approach can be easily adapted to study many other compounds, redox potentials, etc. Additionally, the core technology being proposed for this SBIR could augment other existing NASA instrumentation, such as the highly-flexible PISCES microfluidic instrument, being developed by Peter Willis at JPL. The ability to mix dry chemicals in-situ will benefit all mission instruments which require liquid reagents and standards which would otherwise have a limited shelf life.

The robust nature of INNA, its projected compact size and low-power requirements coupled with its expected sensitivity and long-duration deployments allows it to be integrated into many different research platforms including ocean gliders, buoys, research vessels, autonomous underwater vehicles, underwater observatories, etc. Because nitrate and aquatic nitrite are very important to measure for understanding the oceanic nitrogen cycle, it is a very important quantity to measure. Government agencies have recently been spending hundreds of millions of dollars on large-scale ocean observation networks, such as the Ocean Observatories Initiative. Many of the instruments being purchased for that research are designed to measure ocean chemistry which INNA and INNA-like instruments could measure, but with higher sensitivity than what is being utilized. Additionally, any time there is a need to measure nitrate or nitrite with high resolution, INNA would be cost competitive. This includes healthcare where the measurement of nitrate and nitrite in plasma, urine and other bodily fluids is becoming recognized as important for a variety of reasons including assessment of the NO cycle in organs, markers for bacterial infections, and cardiac health.